冻融作用对不同初始状态基坑稳定性的影响研究

为研究季节冻土区冻融作用对基坑工程的影响，基于考虑冰-水相变的热传导理论、考虑黏聚力的修正剑桥模型和强度折减法，建立了适用于季节冻土区基坑稳定性分析的计算平台。在此基础上，结合具体的试验数据对不同初始状态的基坑算例进行计算，研究季节冻土区基坑冻融前后稳定性和位移的变化情况，并根据土体冻融前后的物理力学参数对上述变化规律作出分析。研究结果表明，冻融作用加剧季节冻土区基坑的局部变形，且土体的初始干重度对变形规律的影响较大，但基坑的整体安全系数并未受到冻融作用的显著影响。存在一个临界干重度γ_d0，基坑土体的初始干重度接近临界干重度时，围护桩水平位移在冻融前后的变化较小，随着土体初始干重度与临界干重度的差距增大，围护桩水平位移在冻融前后的变化量也随之增大。土体的初始干重度越小，基坑围护桩的竖向位移和坑底隆起位移在冻融前后的变化量越大，即土体初始干重度较小的基坑在经历冻融后，围护桩的竖向位移产生显著沉降，但坑底隆起情况有明显缓解。研究成果对季节冻土区基坑工程的设计和施工具有重要意义。

Study on the influence of freeze-thaw on stability of foundation trench under different initial status

In order to study the impact of freeze-thaw on foundation trenches in seasonally frozen regions， a numerical platform for stability analysis is established based on the theory of thermal transport with the consideration of ice-water phase and modified cam-clay model considering cohesion and strength reduction method. By comparing the numerical and experimental data of foundation trench cases with different initial dry unit weights， the deformation and stability as well as the changes in physical-mechanical parameters of the soil induced by freeze-thaw are analyzed. The results show that： 1） the freeze-thaw causes a notable local deformation， 2） the original dry unit weight has a great influence on the deformation characteristics， and 3） the freeze-thaw induces a negligible change in safety factor. The freeze-thaw induced horizontal displacements of piles are relatively small when the original unit weight approaches the critical state （γ_d0）， and the displacements increase when the original dry unit weight deviates from the critical one. The horizontal displacements of piles increase with the increase of the discrepancy between the initial and critical dry unit weights. For the cases with relatively lower initial dry unit weights， larger vertical settlement but smaller basal heave are found. The research results will benefit to the design and construction of foundation trenches in seasonally frozen regions.